Taupo usually sleeps but when it stirs ...

Press, 4 February 1986, Page 6

Taupo usually sleeps but when it stirs ...

The last Taupo volcanic eruption 1800 years ago was so powerful it pushed a giant wave of volcanic material up and over Mount Tongariro at near the speed of sound, a scientist who has made a special study of the volcano says.

Professor George Walker, professor of vulcanology at the University of Hawaii, who is in Auckland for the international vulcanological congress, said Lake Taupo should be recognised for what ,it was — a volcano without a cone.

Though it did not look, remotely like a normal: volcano it has erupted reguarly every 1000 to 2000 years.

Professor Walker, who spent three years in New Zealand, from 1978 to 1981, as a Captain James Cook Fellow, collecting data on the Taupo volcano, presented a key ■paper to the opening session of the congress attended by 480 scientists from 34 countries.

The last Taupo eruption 1800 years ago was one of the most violent known to vulcanologists.

He said that the vent in the lake blew out, and the

volcano poured out molten material and ash at the rate of one cubic kilometre a minute. He said the cloud of molten material, ash and steam probably shot up to 10 to 50km into the atmosphere.

As this material fell, it created a giant avalanche which flowed with such force that it travelled up and over the top of Mount Tongariro, now 1968 metres high.

He estimated that this pyroclastic flow must have reached speeds of up to the speed of sound. The flowing avalanche of Ignimbrite spread outward in a circle from Taupo as far as Rotorua, Taumarunui, Waiouru, even flowing over the Kaimanawa Ranges almost to Napier.

Evidence that the avalanche was powerful enough to reach the top of Tongariro has been found in the layer of Taupo ignimbrite rock left on top of the mountain. Professor Walker thought the Taupo eruption may have been big enough to generate its own hurricane, fuelled by eruption heat and water vapour. The pattern of ash fallout was difficult to. explain without very strong winds.

Professor Walker said the eruption 1800 years ago was a remarkable event The only similar known phenomenon was in Japan 6000 years ago. The eruption was four to five times bigger than the famous Krakatoa eruption last century

which blew apart an Indonesian island.

Although the most recent eruption was a massive explosion it paled into relative insignificance beside the enormous Taupo eruption 20,000 years ago.

He said this was perhaps 100 times bigger than Krakatoa, and 1000 times bigger than the St Helens eruption in the United States in 1980. Earlier Taupo eruptions had sent out pyroclastic flows which reached as far as Auckland.

Even though it was now close to the 2000-year interval since the last Taupo_ eruption, Professor Walker was not too concerned.

“Taupo is a dangerous volcano but. it doesn’t often erupt”